1. Field of the Invention
This invention relates to an automatic focusing device for a video camera which uses a taking lens of a fixed type or a replaceable type.
2. Description of the Prior Art
As the prior art automatic focusing device used for video cameras, there are those shown in FIGS. 1 and 2. In these automatic focusing devices, a taking lens 3 is mounted in a lens mounting section 2 of the camera body 1. The taking lens 3 is provided with a focusing ring 4 for effecting focusing. A gear 5 meshing with the ring 4 can be driven from a motor M mounted in the camera body 1 to move the taking lens 3 in the direction of the optical axis. In the construction of FIG. 1, the motor M is controlled by a motor driving circuit 11, which is in turn controlled by a signal processing circuit 10. A light splitter 6 is provided in the camera body 1 on the optical axis of the taking lens 3. The object data form the lens 3 is thus coupled through an imaging unit 7 and a signal processing circuit 8 and also coupled to the signal processing circuit 10 through a focus detector 9. In the construction of FIG. 2, the motor M is controlled by a signal processing circuit 13, which is in turn controlled by a focus signal extracting circuit 12, which extracts focus signal from an imaging unit 7. In either case, the motor M is controlled by feedback control unit from which a focus signal is produced. In this control, the taking lens 3 is moved in the direction of the optical axis with the rotation of a helicoid, not shown, caused by turning the focusing ring 4.
In these devices, however, the taking lens shares the mechanism of the automatic focusing device, so that the mechanism involved is quite complicated. Further, if the taking lens is not fixed but is replaceable, it is necessary to provide a form of driving which has versatility with respect to various interchangeable lenses that may be prepared. In this case, therefore, it is inevitable that the mechanism is more complicated and that the weight and price are further increased. Further, movable parts such as focusing ring and gear are found on the outside of the camera body. Therefore, these parts are liable to interfere with an object and be damaged, thus sometimes disabling the taking.